1. Field of the Invention
The present invention relates to an improved method and apparatus for relating fuel use in a combustion system to outdoor air temperature and an improved method, apparatus and system for scheduling fuel deliveries and detecting fuel leaks for fuel combustion systems and measuring the fuel efficiency of building modifications.
2. Description of the Prior Art
Current methods used by liquid fuel suppliers such as fuel oil and propane companies typically collect information on outdoor air temperature that is used to calculate heating degree days. Heating degree days are generally defined as 65° F. minus the average daily temperature. For example, if the average outside temperature for the day is 40° F., then the number of heating degree days for that 24-hour period is 65−40 which equals 25. The heating degree day method is commonly used by fuel suppliers to estimate when fuel deliveries are needed by evaluating the remaining fuel in the tank as heating degree days accumulated during the heating season. Typically, fuel deliveries are scheduled based on tracking simple heating degree-days which reflect how much heating is required based on outdoor air temperature. As the outdoor temperature drops, heating degree-days increase and more fuel is used.
Fuel marketers use past fuel use and heating degree day data to estimate fuel use and establish k-Factors which are heating degrees day per gallon. These apply only during the heating months. Other estimates are used to modify these factors during periods of heating and non-heating, but with limited accuracy and reliability. These factors are frequently installed in computer systems that monitor fuel use. A fuel delivery target is set, elapsed heating degree days are monitored, and when the K-Factor indicates that the delivery target is reached, a fuel delivery is scheduled.
The conventional heating degree-day method is a poor indicator of actual fuel used especially during intervals of both space heating and non-space heating that commonly occur in buildings. Uncertainties in fuel use prediction on the order of 25% to 50% are commonly observed with the simple heating degree day method. This lack of precision severely limits optimum deliveries in most buildings. In some cases, it over-predicts the remaining fuel in the tank. In other cases it under predicts the remaining fuel. When it over estimates the remaining volume of fuel in the tank, smaller than optimum fuel deliveries occur. When it under-estimates the remaining volume of fuel in the tank, customer run-outs occur which are highly undesirable and costly. The overall result of this inaccuracy of the simple heating degree day method is that typically, on average, only about 150 gallons of fuel are delivered to 275 gallon fuel tanks on each fuel drop. This large safety factor is created by the predictive inaccuracies of the simple heating degree day method and substantially increases fuel delivery costs. As a result there remains a need in the art for improved methods to predict the remaining fuel in a fuel tank of a combustion system.